Several proposals have been made to mount certain function switches on the vehicle steering wheel in order that they may be more conveniently available for actuation by the vehicle operator. Such switches may be those presently provided elsewhere, such as the cruise control, windshield wiper, windshield washer, headlamps dimming and turn signal switches. See, for example, U.S Pat. Nos. 3,670,174 and 4,340,824. The systems disclosed in each of these patents transmit distinct voltage levels associated with each switch closure through the slip ring of the vehicle horn circuit to decode circuitry which controls load devices intended to be energized in response to switch closure. There are several problems associated with this prior art approach. In order to maintain a quality connection and minimize voltage variations, an expensive slip ring is often required. Further, the horn switch is usually encoded along with the added switches because of the fairly narrow voltage range otherwise available for encoding the switches. This encoding of the horn switch degrades the reliability of the horn circuit. For example, under a low voltage condition it may not be possible to energize the horn.